A tripod is a camera stand. It has three legs, and a 1/4″-20 screw or a 3/8″-16 screw to securely mount the camera to the top. Some tripods include non-removable heads, others are sold without heads. Early photographers adapted for their own use the tripods used by surveyors. In 1900 two standard tripod types existed, one common in the UK for field cameras, the other type already with screw as camera mount.